In measuring blood sugar levels, it is desirable to employ a method which accurately reflects the average long-term level rather than short-term fluctuations; the method should be simple and economical. Since soluble blood sugar levels can exhibit extensive short-term fluctuations in both diabetics and in normal subjects, other measures of blood sugar levels have been investigated. One such alternative measure is the hemoglobin fraction termed HbA.sub.1c. This minor fraction is formed by a slow non-enzymatic condensation of glucose with the N-terminal amino group of the .beta. chain of HbA.sub.0, the main hemoglobin component. The observation made by Rahbar (1968) Clin. Chim. Acta 22:296-298; Trivelli et al. (1971) N. Engl. J. Med. 284, 353-357; and Gabbay et al. (1977) J. Clin. Endocrinal. Metab. 44, 859-864, that the HbA.sub.1c fraction is elevated 2-3 fold in patients suffering from diabetes mellitus has led to the use of measurement of the HbA.sub.1c fraction by ion exchange column techniques as a diagnostic tool to follow diabetic control.
Another method of quantifying the A.sub.1c fraction has been described in Fluckiger et al. (1976) FEBS-Lett. 71:356-360. Glycosylation of the hemoglobin fraction at sites other than the amino terminal position of a hemoglobin chain is quantified by heating the protein under acidic conditions and colorimetrically measuring the generated furfural compounds with 2-thiobarbituric acid.